This invention relates to a vibrator assembly, more particularly, but not exclusively, to a vibrator assembly for use with equipment used in minerals classification and beneficiation, such as screens and feeders, hereinafter referred to as screens.
Screens are widely used in the classification of solids. In minerals processing plants and quarries, large quantities of ore have usually to be classified as speedily and cost effectively as possible. In such plants it is thus common to find banks of super adjacent screens which are subject to vibration. Compactness is obtained by using banks of screens while screening efficiency is enhanced by vibration of the screens. When vibrated, a high volume throughput is obtained over a screen and is subjected to screening.
A number of methods are used to achieve vibration of screens, these may take the form of a vibrator secured on either side of a screen bank, usually to the side plates in which the screens are secured, the bank being mounted in turn on coil springs, rubber mounts or similar devices. Vibrators sometimes take the form of an electric motor driving an eccentrically weighted shaft.
There are most commonly two methods of vibration applied to the vibrating screens: the circular movement, or the linear movement.
Circular movement is more popular due to lower costs than the linear movement. It is most commonly obtained by rotating vibrators placed on the side plates or on a beam over or under the screening surface.
The linear movement is widely believed to have many advantages in the screening process. However, due to its higher production cost, their applications have been limited. The linear movement is usually obtained by two shaft geared to be synchronised and with the vibrating mechanism placed on beams over or under the screening surface or fixed directly to the side plates of a box construction of similar width to the screen.
Another way to obtain the linear movement by means of two shafts is by using the phenomena of self-synchronisation, when the two shafts do not need gears for synchronisation, it being sufficient that they are placed adequately and rotated with inverted rotation one to the other (one clockwise and the other counterclockwise). It is the most cost effective arrangement of self-synchronisation to place the vibrators fixedly on each side plate with the vibrating counterweight parallel to the side plate plane, and inclined in adequate angle.
This type of assembly has encountered difficulties due to high stresses introduced into the screen structure and only few manufacturers have made use of such arrangement, with limited success.
WO 93 19859 A (Sweco, Inc) describes a screen assembly with a screen secured between a pair of sideplates. A rotary eccentric vibrator mounted to each sideplates inclined to provide unidirectional elliptical vibratory motion to the assembly. Elliptical movement is less efficient than linear movement and the stresses introduced into the sideplates will probably be slightly less than those induced by linear movement. However, the applicant considers that the screen assembly disclosed will not endure with screens longer than 1 m due to stresses that will be developed in operation. These stresses will be particularly significant on the mounting plates for the vibrators and the mountings to the sideplates due to the turning moment caused by the vibrators. This patent further discloses a structural tube extending between the sideplates typical of many screen assemblies. The applicant views this tube as being ineffective in preventing damage to the sideplates as stresses will be transmitted through the sideplates prior to reaching the structural tube.
EP 0 185 409 A (Flow Control Service BV) discloses a pair of screen mats held in a tensioned condition between a pair of sideplates. Transverse tubes hold the sideplates in a spaced condition and assist in providing structural strength to the assembly. A rotary vibrator is secured centrally on each sideplate. This patent discloses the problem of stress fractures forming on screening apparatus and proposes to solve this problem by means the complex mounting arrangement for the vibrators. The applicant considers that fractures will still occur in the sideplates due to the transmission of the vibratory forces and that these will only be mitigated to a small extent by the transverse tubes.
U.S. Pat. No. 5,802, 965 (Lin) discloses a frame to which are secured a pair of vibrators and which in turn supports a bean sprout treating surface above the vibrators. The applicant is of the view that this assembly will have insufficient robustness for heavy loads.
FR 2 604 376 discloses a damper for vibrations between motors and screen assemblies but does not describe the manner in which a motor can be mounted to a screen or a manner by which stresses on screen assemblies can be reduced.
It is the object of this invention to provide a vibrator assembly which will at least partially alleviate some of the abovementioned problems.
In accordance with this invention there is provided a vibrator assembly comprising a pair of vibrators held in spaced relationship by a frame to be securable to opposite side plates between which at least one screen extends, the frame shaped to transmit between the vibrators loadings generated by the vibrators which, in use, impart undesirable stresses to the screen assembly.
Further features of the invention provide for the screen to have a pair of side plates between which at least one screen extends; and for each side plate to be secured to a vibrator.
Further features of the invention provide for the frame to transmit loadings which are transverse to the side plates; for the frame to transmit loadings such that loadings transverse to the side plates are balanced; and for the vibrators to be arranged to impart linear motion to the screen assembly.
Still further features of the invention provide for the frame to have at least one, preferably two cross members, for the or each cross member to be tubular, preferably circular in cross-section; for the ends of the or each cross member to be pinched; for the or each cross member to operatively extend between the side plates; and for the or each cross member to have a flange at each end thereof to which a side plate is securable.
Yet further features of the invention provide for each vibrator to be secured to a flange securable to the or each cross member; for each vibrator to be secured to a carrier extending from the respective flanges; for each carrier to extend normally to the flange associated therewith; for the carriers to extend in a plane intersecting the longitudinal axis of the or each cross member; and for the carriers to be elongate with a vibrator secured to one end thereof and tapering towards the other end thereof.
Further features of the invention provide for each vibrator to include at least one, preferably two eccentrically weighted discs rotatably mounted on an axles to be driven through a shaft by a motor; for each motor to be secured to a side plate; alternatively for each motor to be free-standing; and for two or more screens to extend between the side plates in super adjacent configuration.
The invention further provides a screen assembly comprising at least one screen extending between a pair of side plates and secured to a vibrator assembly substantially as defined above.
The invention also provides a self-supporting frame for a vibrator assembly substantially as defined above.
A method of imparting linear vibration to a screen assembly comprising, mounting a screen assembly between a pair of vibrators operating the vibrators to impart linear motion in parallel planes to the screen and interconnecting the vibrators to dissipate between them loads generated transverse to the parallel planes of movement.
Further features of the invention provide for side plates on the screen assembly to be secured to the vibrators; for the vibrators to be interconnected by at least one cross-member extending between the side plates; and for the vibrators to be secured to the or each cross-member by fasteners.